Psi, << sy, >> particle, also called a J particle, is a type of subatomic particle. A psi particle consists of a quark and an antiquark. A quark is an elementary particle that combines with other quarks to form such familiar particles as protons and neutrons. An antiquark has the same properties as a quark but carries an opposite electric charge. In a psi particle, the quark is a charm quark, and the antiquark is an anticharm quark. See Quark .
The structure of a psi particle is similar to that of a hydrogen atom. Both a hydrogen atom and a psi particle consist of two particles bound together. However, the components of a hydrogen atom—a proton and an electron—are bound together by electromagnetism. The quark and antiquark of a psi particle, on the other hand, are held together by the strong nuclear force, also called the strong interaction (see Force (The strong force) ). Just like a hydrogen atom, a psi particle carries no electric charge.
The psi particle was discovered in 1974 by two groups of American physicists working independently at the Stanford Linear Accelerator Center and Brookhaven National Laboratory. The discovery of the psi particle and the study of its properties provided strong evidence for the existence of the quark.
